Described below is a contactless and infrared-optical methods and systems for determining the emissivity.
Here, the emissivity E is defined as the ratio of the radiation power of the object to that of an ideal blackbody emitter. The value of the emissivity E for real objects lies between the extreme values 0 for perfectly reflecting objects and 1 for an ideal blackbody.
The emissivity E can constitute a characteristic variable for the aging of materials. Therefore, knowledge of the emissivity E or the change thereof over time or operating duration of a material allows deductions to be made in respect of the aging behavior of the material.
When determining the temperature of objects, it is likewise to be noted that the radiation emitted by an object is dependent not only on the temperature but also on the emissivity E thereof. Furthermore, in various applications of thermography, it may be necessary to know the emissivity E of the thermographed object in order to be able to determine the level of the expected signals and/or the influence of interference signals from the surrounding radiation.
By way of example, document U.S. Pat. No. 7,133,126 B2 discloses an optical method for determining the thickness of coatings on a heat exchanger.
Document U.S. Pat. No. 7,409,313 B2 discloses a method for determining the thickness and thermal conductivity of an insulating layer of an object, in which optical pulses are reflected by the insulating layer and evaluated by an optical measurement system.